A manhole is usually placed in street as a top opening for providing easy access and maintenance to the underground structure such as pipe line or sewer. The manhole is sealed by a manhole cover to avoid the falling of pedestrian or object. As shown in FIG. 5, a traditional manhole assembly may consists of a skirt (72) and a manhole cover (71), seated on a shoulder of the skirt (72). The manhole cover is commonly made of solid steel to support the weight of vehicles which pass over everyday. However, heavy cover also requires greater strength when it has to be removed. Maintenance staff is usually equipped with basic tool such as crowbar to lift the lid. A hole (73) is set on the cover (71) for receiving and engaging the tool. By assistance of the tool, the force needed to remove the cover is slightly reduced but it still requires a strong person for operating; and the disengagement of the crowbar with cover may injure the worker. Further, a slit (74) is usually kept for the expansion of metal cover (71), said slit (74) is easily clogged with matter (75), such as dust or other impurity, making the cover (71) being difficult to be opened. Moreover, the traditional manhole assembly doesn't provide any waterproof feature, which may allow liquid penetrate the manhole, corroding and damaging the equipment or device therein, and endangering the safety of the personnel who performs maintenance. Therefore, to provide a manhole cover heavy to bear the car passing by and easy to lift with water tight feature has become the objectives of the present invention.